1. Field of the Invention
The present invention relates to a cooling apparatus for a motor means and, more particularly, to a cooling apparatus for a motor means incorporated in a blower system.
2. Description of the Prior Art
Generally, the overheating of motors is caused mainly by heat generated in an armature of a motor; therefore, an effective measure for preventing the overheating of the motor is to cool the armature.
A known cooling arrangement has a pair of holes formed in radially opposing portions of a peripheral wall of a motor housing encasing an armature or, alternatively, in both axial end walls of the motor housing. Cooling air is introduced through one of these holes and, after flowing around the armature, is discharged to an outside of the motor through the other hole.
Japanese Utility Model Laid-open Publication No. 72107/1977 discloses an arrangement for cooling a motor used in a blower system wherein the motor has a housing, an armature fixed to a motor shaft and housed by the housing, a blower fan attached to one end of the shaft projecting to the outside of the housing through one of two axial end walls, and a blower casing encasing the blower fan. An air introduction hole is formed in a portion of the housing remote from the blower fan, while an air discharge hole is formed in the portion of the housing being adjacent to the blower fan and facing a space in which the air pressure is lower than that in a space around the air introduction hole. In operation, the cooling air is induced through the air introduction hole by the lower pressure in the space around the air discharge hole and, after flowing around the armature to cool it down, discharged to the outside of the motor through the discharge hole.
Generally, in a motor used in a blower system, a commutator and brushes are provided at the space in the motor axially opposite to a blower fan in order to prevent a noise transmission to the outside through the fan casing, which is produced as a result of the sliding contact between the brushes and the commutator. Consequently, the air introduction hole is inevitably positioned at a position in opposition to the commutator.
It is generally impossible to eliminate the moisture and the dust from the air introduced through the air introduction hole without an additional elimination means. The moisture and the dust both contained in the introduced cooling air directly collide with and attach to the peripheral surface of the commutator. As the motor operates for a long time under such a condition, the moisture and the dust fill the gaps between adjacent copper elongate strips which are arranged on a core surface at a constant pitch in the circumferential direction. Consequently, the copper elongate strips are electrically sshort-circuited and an overcurent flows to rapidly increase the calorific value. The electric short-circuiting also generates sparks between adjacent copper elongate strips to roughen the surfaces thereof. This roughening undesirably deteriorates the out of roundness of the commutator and the sliding friction between the commutator and the brushes is increased to generate noise.